Nucleoside Cation Radicals: Generation, Radical-Induced Hydrogen Atom Migrations, and Ribose Ring Cleavage in the Gas...

Area of Science:

• Physical Chemistry
• Mass Spectrometry
• Computational Chemistry

Background:

• Nucleoside chemistry is fundamental to understanding DNA and RNA.
• Gas-phase ion chemistry provides insights into fundamental reaction mechanisms.
• Radical-initiated reactions in biomolecules are crucial for various biological processes.

Purpose of the Study:

• To investigate the gas-phase chemistry of nucleoside ions with a 2'-O-acetyl radical group.
• To elucidate the hydrogen transfer pathways and kinetics in 2'-O-acetyladenosine cation radicals.
• To explore radical-driven dissociations in other nucleoside ions.

Main Methods:

• Multistep collision-induced dissociation (CID) to generate radical ions.
• Deuterium labeling studies to identify hydrogen transfer sites.
• Born-Oppenheimer molecular dynamics and density functional theory (DFT) for theoretical calculations.
• UV-vis action spectroscopy to characterize ion structures.
• Rice-Ramsperger-Kassel-Marcus (RRKM) and transition-state theory (TST) for rate constant calculations.

Main Results:

• 2'-O-acetyladenosine cation radicals preferentially undergo hydrogen transfer from the 4'-position of the ribose ring to the acetoxyl radical.
• Hydrogen transfer is kinetically controlled, with product formation influenced by transition-state energies.
• Significant isotope effects and quantum tunneling were observed, affecting reaction branching ratios.
• UV-vis action spectroscopy revealed a mixture of isomers for the 2'-O-acetyladenosine cation radicals.
• Radical-driven dissociations were observed for other nucleoside ions, but nucleobase loss or protonated nucleobase formation dominated.

Conclusions:

• The gas-phase chemistry of 2'-O-acetyladenosine cation radicals is characterized by kinetically controlled 4'-H transfer to the acetoxyl radical.
• Computational and experimental methods provide a detailed understanding of hydrogen migration mechanisms, isotope effects, and quantum tunneling in these systems.
• Radical-initiated reactions in nucleoside ions exhibit diverse dissociation pathways depending on the specific nucleoside and radical group.